Conventional navigation systems have a function of searching a route to a destination and guiding the searched route to a user. The navigation systems also have a function of detecting the position of a vehicle (subject vehicle) to draw a map data around the position of the subject vehicle on a display, displaying a mark of the subject vehicle on the displayed map data, and scrolling the map in conformity with variation of the position of the subject vehicle.
Furthermore, recent navigation systems are provided with a communication function of communicating with external servers and networks, a reproducing function of reproducing audio/video data of CD, DVD, etc., a receiving function of receiving television broadcast or radio broadcast, etc. Particularly by using the communication function, the user of the subject vehicle can acquire information on vehicular accidents and traffic jam occurring at the outside of the subject vehicle on a real-time basis, and acquire new map data, data of facilities, etc. from a map distribution server or the like, thereby enhancing the convenience for users.
A function of receiving weather information transmitted from an outside source to display rainfall information or fair weather information on the basis of the weather information or predict places at which traffic regulation or risks may occur, and searching a guide route to a destination while avoiding these places is known as an example of utilization of the communication function.
Map display devices in which the map data of a map is on a display while the map is scrolled on the display are known. In some of these display devices, an area name such as a prefecture name or the like is scrolled at a lower speed than a map scroll speed when a map is scrolled (for example, JP 2004-126338A). The position at which the area name is displayed is preset in the map data.
In some of these map display devices, even when only a part of a polygon is displayed on a display screen, the polygon name thereof is displayed on the display screen (for example, JP 09-330024A). Specifically, the map display device is provided with a road map data containing polygon data in which a polygon name “AB park” is registered for plural registered positions Pn, Pn1 to Pn11 in a polygon, a display area of a road map is set and a polygon contained in the road map is extracted. Then, the road map in the display area is displayed on the basis of the road map data, and the name of the extracted polygon (polygon name) is displayed at any registered position contained in the display area.
In the above two devices, area names or polygon names can be displayed on the display screen while superposed on areas having fixed shapes such as administrative sections such as prefectural and city governments, parks, etc. However, it is difficult to display names or icons on the display screen while the names or the icons are superposed on areas whose shapes are fluctuating (variable) like weather phenomena, etc. For example, when the shape of an area representing weather information has an out-of-area portion at the inside thereof like a donut shape or the like, the name or icon of the area concerned may be erroneously displayed on the out-of-area portion. In this case, the out-of-area portion may be misidentified as the area representing the weather information concerned.